"pub cache repair" prints a more detailed summary.

lib/src/source/cached.dart

Index: lib/src/source/cached.dart
diff --git a/lib/src/source/cached.dart b/lib/src/source/cached.dart
index 3775aa910728d1572f165d5600ab20769a58a8c7..bfe0382e796e5cfb1ea787394f747cbebc011052 100644
--- a/lib/src/source/cached.dart
+++ b/lib/src/source/cached.dart
@@ -67,7 +67,8 @@ abstract class CachedSource extends Source {
   /// Reinstalls all packages that have been previously installed into the
   /// system cache by this source.
   ///
-  /// Returns a [Pair] whose first element is the number of packages
-  /// successfully repaired and the second is the number of failures.
-  Future<Pair<int, int>> repairCachedPackages();
+  /// Returns a [Pair] whose first element is the packages that were
+  /// successfully repaired and the second is the packages that failed to be
+  /// repaired.
+  Future<Pair<List<PackageId>, List<PackageId>>> repairCachedPackages();
 }